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The Engineered Aggregate Pier System


Engineered Aggregate Piers are a cost-effective solution to foundation support on soft soil sites and provides an excellent alternative to deep piles/caissons and overexcavation and replacement filling.


Engineered Aggregate Piers are constructed in a pre-excavated cavity with specialized ramming equipment that imposes significant lateral prestress into the undisturbed soils surrounding the element.

The combination of constructing the piers in pre-excavated cavities and the lateral stress build-up that results from the specialized ramming equipment, are the key elements that set Engineered Aggregate Piers apart from other aggregate pier or stone column systems. They are the primary factors accounting for the phenomenal success in controlling foundation settlements in soft soils.

Pier cavities are typically excavated by conventional drilling techniques, using either truck-mounted auguring equipment or "dangle drill" equipment mounted on an excavator or crane.

Drilled cavities for Engineered Aggregate Pier elements typically range from 18" to 36" in diameter.

With the use of casing, Engineered Aggregate Pier elements can be constructed below ground water in all soils ranging from peat to loose clean sands to soft clays.

Aggregate used for pier construction is typically high quality crushed rock, such as used for highway base course construction. Lower quality aggregate can be used so long as compacted characteristics are relatively uniform and are defined by field testing. For liquefaction mitigation, free-draining aggregate can be used so the pier element also functions as a drain to relieve excess pore water pressures.

Engineered Aggregate Piers are constructed in lifts of about 1 to 2 foot thickness (depending on ramming energy used), with each lift rammed vertically and laterally using the specialized tamper. Within 15 seconds of tamping, a lift can receive over two times the compactive energy that is put into the maximum density laboratory test (ASTM 1557).

Since Engineered Aggregate Piers elements are constructed in pre-excavated cavities, there is essentially no remolding of the surrounding soils, as occurs with other stone column techniques that involve complete soil displacement. Hence, with the Engineered Aggregate Pier technique the surrounding soils cannot experience strength loss due to the construction methods, but rather gain a significant increase in stiffness as each lift of aggregate is rammed. Other aggregate pier systems can not achieve this level of stiffness increase!

By constructing Engineered Aggregate Pier elements in clusters spaced from about 1½ to 3 diameters apart, the GeoRam® reinforced soil mass experiences significant permanent prestressing, which greatly improves its strength and consolidation characteristics (extending several feet beyond the outside piers). Hence, the so-called "group effect" is very desirable for the GeoRam® system because it improves performance (whereas, in the design of pile foundations the group effect is normally avoided because it tends to reduce individual pile capacities).


The GeoRam® Engineered Aggregate Piers system is applicable in any situation where a significant increase in stiffness and/or shearing strength of a soil mass will improve engineering performance. This includes:

Spread footings -- Increase in bearing capacity and reduction of settlemen

Floor slabs/mats -- Improve subgrade uniformity and reduce settlements

Slopes -- Increase in factor of safety for stability

Excavations -- Increase in temporary support

Note the significant lateral stress increase in the soils surrounding the Engineered Aggregate Pier element.

THIS is the key to the incredible success of Engineered Aggregate Piers have in reducing settlement in soft soils.
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